Mine use bungy cords to hold the boards in place and they work fine. You just need to mount them at just the right angle: too vertical and it's tough to get your boards in and out and too far horizonal and the weight (and bumps) will eventually pull or break them off. Slightly less than 45 degrees is about right.

Mine have been totally secure. They dont even move at all because the tines on the rack fit in between the bindings and keep it from sliding front to back and the bungees keep the boards from bouncing up and out. Just make sure you get a beefy rack-the first one I had was tilted too far horizontal and actually snapped the bolts (with 2 boards attached) while I was on my SkySki. Luckily I was on the other side of the wake at the time otherwise I would have been in trouble. I have a Wake Designs rack now and it works great.

I've got the Wake Designs racks which were originally mounted on our pylon, and then we rigged them to the new tower. To answer your question, yes they hold fine. I have never had a problem with them, nor have anyone else I know had any problem with any bungee system.